1. Field of the Invention
The present invention relates to an apparatus and a measurement method.
2. Description of the Related Art
The color of an image formed by an image forming apparatus using an electrophotographic method, electrostatic recording method, or the like, such as a copying machine, laser printer, or facsimile apparatus, varies with changes in various physical parameters. For example, since the latent image potential, toner replenishment amount, transfer efficiency, and the like change with variations in temperature, humidity, and the like, the amount of toner adhering to the photosensitive drum and the transfer belt is not constant.
Japanese Patent Laid-Open No. 8-327331 discloses a method of measuring the thickness (layer thickness) of a toner patch by using a laser displacement gauge. More specifically, a spot light beam irradiates an image carrier which carries the toner patch. The reflected light is then formed into an image at a position corresponding to the thickness of the toner patch on the image carrier. A PSD (Position Sensing Device) or the like detects a change in the image formation position of light when the toner patch passes through the irradiation position of the spot light beam, thereby measuring the thickness of the toner patch. Feedback control is performed for an image formation process based on the thickness of this toner patch.